I highly recommend www.e-reading.club/top100_rating_books.php?type=3
You can sort by rating and browse by book type and check books by certain authors. I just downloaded a couple years worth of reading here recently. BTW I think they may all be free too (older?). I’ve looked mainly for older stuff though.
also http://librebook.me/
Here is list only of classic book titles for kids, but a quick google search for the title will bring you to a free download:
http://www.razumniki.ru/chtenie_sem.html